Update asset targets for canary/beta/release.

Assumptions for this PR:

* canary -> 'master' branch
* beta -> 'beta' branch
* release -> 'stable' | 'release' branch

Standard targets (non-tagged revisions) are:

```ruby
EmberDev::Publish::Asset.new('ember.js', :build_type => :canary).targets_for('.js')
=> ["ember-latest.js",
    "latest/ember.js",
    "canary/ember.js",
    "canary/daily/20130901/ember.js",
    "canary/shas/600c5e6e0fd60903ad9cdc79839d338c7f994ec7/ember.js"]

EmberDev::Publish::Asset.new('ember.js', :build_type => :beta).targets_for('.js')
=> ["beta/ember.js",
    "beta/daily/20130901/ember.js",
    "beta/shas/600c5e6e0fd60903ad9cdc79839d338c7f994ec7/ember.js"]

EmberDev::Publish::Asset.new('ember.js', :build_type => :release).targets_for('.js')
=> ["stable/ember.js",
    "release/ember.js",
    "release/daily/20130901/ember.js",
    "release/shas/600c5e6e0fd60903ad9cdc79839d338c7f994ec7/ember.js"]
```

Tagged targets are:

```ruby
EmberDev::Publish::Asset.new('ember.js', :build_type => :release, :tag => 'v999').targets_for('.js')
=> ["stable/ember.js",
    "release/ember.js",
    "release/daily/20130901/ember.js",
    "release/shas/600c5e6e0fd60903ad9cdc79839d338c7f994ec7/ember.js",
    "tags/v999/ember.js"]
```